C++最大堆实现priority_queue优先级队列（算法导论）

max_heapify与build_max_heap过程与heapsort一样

#include <iostream>
#include <cstdio>
#include <ctime>
#include <cstdlib>
using namespace std;

const int INT_MIN = -(1 << 31);
inline void swap(int &a, int &b) { int t = a; a = b; b = t; }
inline int parent(int i) { return (i-1) >> 1; } //下标都是从0开始，与算导上不一样
inline int left(int i) { return (i << 1) + 1; }
inline int right(int i) { return (i << 1) + 2; }

int heap_size, heap_length; //heap_length是数组元素个数，heap_size是有多少个元素存储在数组中。0<=heap_size<=heap_length

void max_heapify(int *a, int i) { //O(lgn), 维护heap的性质，使得以下标i为根结点的子树重新遵循最大堆的性质
int l = left(i), r = right(i);
int largest = 0;
if (l < heap_size && a[l] > a[i])
largest = l;
else
largest = i;
if (r < heap_size && a[r] > a[largest])
largest = r;
if (largest != i) {
swap(a[i], a[largest]);
max_heapify(a, largest);
}
}

void build_max_heap(int *a) { //O(n), 对树中非叶结点都调用一次 max_heapify
heap_size = heap_length;
for (int i = heap_length/2 - 1; i >= 0; --i) //可以证明下标为n/2-1到0的结点为非叶结点
max_heapify(a, i);
}

int heap_maximum(int *A) {
return A[0];
}

int heap_extract_max(int *A) {
// if (heap_size < 1)
// return;
int max = A[0];
A[0] = A[heap_size-1];
--heap_size;
max_heapify(A, 0);
return max;
}

void heap_increase(int *A, int i, int key) {
if (key < A[i])
return;
A[i] = key;
while (i > 0 && A[parent(i)] < A[i]) {
swap(A[i], A[parent(i)]);
i = parent(i);
}
}

void max_heap_insert(int *A, int key) {
++heap_size;
A[heap_size-1] = INT_MIN;
heap_increase(A, heap_size-1, key);
}

bool empty() {
return heap_size == 0;
}
int main()
{
srand(time(NULL));
while (scanf("%d", &heap_length) != EOF) {
int a[heap_length];
for (int i = 0; i < heap_length; ++i)
a[i] = rand() % heap_length;
build_max_heap(a); //构建最大堆
while (!empty()) {
printf("%d ", heap_extract_max(a));
}
printf("\n");
}
return 0;
}